Other Asynchronous/Synchronous Sequences In Dsc (Bsc-Attached) Mode; Asynchronous Nack In Dsc (Bsc-Attached) Mode - IBM 6400 Programmer's Reference Manual

IPDS for Control Units
Other Asynchronous/Synchronous Sequences in DSC
(BSC-Attached) Mode
The following charts show what can happen if the host application issues a write
type (Text) command after the printer sends a Device End. These sequences are
not recommended.
Asynchronous NACK Sequences in DSC (BSC-Attached) Mode: In Figure 41, the
host sends text to the printer after a Device End while the printer has an
asynchronous NACK pending.
Figure 41. Asynchronous NACK in DSC (BSC-Attached) Mode
Note: If the first text section is the end-of-chain, and the host does not read the
NACK before sending more text, then the printer loses the pending NACK and
processes the second text section, as illustrated in Figure 41. If the first text
section is not end-of-chain, the printer ignores the second text section sent by
the host and resends the NACK.
Synchronous NACK Sequences in DSC (BSC-Attached) Mode: In Figure 42, the
host sends text to the printer after a Device End while the printer has a
synchronous NACK pending.
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Appendix B. Summary of IPDS for Control Units